Dipel dust. It is Bt bacteria and is the primary pesticide for cabbage loopers - the worms. It is also sold as Thuricide in a liquid form. Otherwise the best method is row covers/insect barrier.

You'll find many discussions here about both methods.

Dave

I like to use row covers but you have to be sure to get it on before you see the moths. Otherwise they lay their eggs on the underpart of the leaves and you still get the worms when they hatch. If I don't get it done before I see the moths, I use Dipel dust which works very well, too - just more hassle reapplying every week or two and after rain.

Some take it as a sign that the plants are weak. Low sulphur in the soil for starters.

I grow collards year around & just pick the badly eaten leaves for the compost pile & eat the good ones.
I have had plants live for four years.
I do hand pick any bugs I find on the plants.

It's important to identify which caterpillar/moth you are talking about. I've sometimes had to resort to placing the pupa (cocoon) in a jar to see what moth comes out.

Someone mentioned cabbage loopers. The adult/moth is dark in color. I've dealt with them (and melonworms), and Bt worked great. They went crazy for the zucchini plants, but completely ignored the kale plants a foot away.

Last season, I was asking the same question, because they were stripping my kale to the stem. Bt might have worked better but we got a storm every other day for several weeks, and I couldn't keep up with re-applying the Bt every time. I noticed that the Lacinato kale was strongly favored over the Red Russian variety, but once the Lacinato was stripped, they'd go after the other. If it rains a lot in your area, row covers might be the best bet.

I plan to try something else that I heard about, though. Apparently, "glazed" collards have a coating on the leaves that makes them resistant to the little buggers. Cascade Glaze is a recently developed open-pollinated variety for shorter seasons. But the old fashioned Green Glaze aka Greasy Glaze collard is said to also be more resistant to cold than you might expect for a typically Southern crop. Supposedly, this coating on the leaves (harmless to humans) also protects them somewhat from the cold.

Cabbage Looper moths are white with hints of grey and yellow in my area. They flit around the garden, landing very briefly on the plants. On each one, they lay an egg which quickly becomes a caterpillar, and they love brassicas and cole crops. I favor row covers, but any of the Bt products will help if you're not opposed to spraying. There are stronger chemicals available I'm sure, but as an organic grower I am not familiar with them. I am not familiar with raising collards, but kale should be left in the garden as long as possible - I frequently harvest kale long after the loopers have ceased to be a problem. I'm not selling my outdoor kale now, but I'm still picking it to eat.

Here is a link that might be useful: What mine look like

Sounds like they might be imported cabbage worms. (Imported from England, thank you very much.) Other control methods I've heard about in addition to the more effective ones stated above:
Spread corn meal around the plants (the caterpillars are supposed to eat it, swell their stomachs, and die)
Catch the moths with a butterfly net
Get kittens who love to catch the moths and eat them :)
Before eating the leaves, soak in salt water (so the caterpillars will die and fall off and you won't have to eat them.)

DEFINITELY more of a problem with weak plants. I had kale growing two different places, one with much better soil. The caterpillars barely noticed the healthier plants, and they had apparently gotten under my row covers over the less healthy plants, and the result was an absolutely comical stripping job (I could laugh because I had the healthy kale in the other bed :) )

I've had kale plants produce for years without bolting or flowering, so you may well find a nice spring crop of collards growing from the old stems. Also, when it gets cold is when those nasty things finally die, and you get pest free leaves again! Next year try waiting before you cut the plants and see if the leaves clear up.

Row covers--cheap, easy, effective, reusable.

When we find yellow jacket nests close to the garden, we leave them alone. New ones seem to appear in midsummer at about the time I plant fall brassicas. I set out the plants under row covers, mostly for grasshopper protection, but in Sept. I open the covers and let the yellow jackets take care of the cabbageworms. They do an awesome job.

For a long-term/no-work solution, encourage paper wasps in your garden. I put up numerous wren houses in the garden which the paper wasps also like to use as nest sites. They are generally non-aggressive even near their nests, but I still place the bird houses in low-traffic areas. The paper wasps are NEVER aggressive in the garden when searching out green cabbage worms.

For the last five years I have had no cabbage worm damage during the main season and I do nothing. My garden is, however, 100% organic. In late fall as the paper wasps die off, I will have some cabbage worm damage, but it is minimal at that time.

Bellatrix

Bellatrix -- this is brilliant! I *hate* accidentally cooking cabbage worms for dinner. Are the wren houses the only thing you do to draw the paper wasps? I have some kind of wasp trying to live in my clothes line poles, but the neighbor boys keep taking the nests out (and getting stung alot, but WV kids are tough) I'll go google paper wasps and see if they look familiar.

Elisa

I had caterpillars on one patch of Swiss chard this winter. A single Bt dusting took care of them. Strange that they didn't bother the other plantings that were nearby. I grow chard for food as well as ornamentation in the garden and flower beds, so row covers aren't an option for me.

Any type of bird house will work, particularly if they are hung in the shade. Again, an out of the way place is best. My neighbor one street over has about 50 birdhouses hanging on his porch and trees. I think that my be part of my paper wasp source. Gourds cut out for bird houses also work very well. They also like nesting on a shed over-hang or under the roof of any small structure.

Any type of wasp will help with your cabbage worms, so protect them all. Paper wasps are very efficient and non-aggressive. Yellow Jackets are fantastic, but not as human friendly. They look alike to most people, but are not. Yellow Jackets nest in holes usually and paper wasps in paper nests hung under shed roofs or bird houses. Google can show you the difference.

I usually don't like linking to wikipedia, but it does show the brown native paper wasp. If you see these, protect them at all cost. They are very gentle and being pushed out by the introduced European paper wasp.

An old German (maybe Pennsylvania Dutch) saying is that a farmer who knocks down his wasp nests will have no cabbage crop. :)

Bellatrix

Here is a link that might be useful: Paper wasp

Wow -- so glad to learn this about the paper wasps. I sure hope they come back, after I let those boys harrass them! It was because a hive of yellow jackets chased my husband, stung him up, and made him swell up in a scary way, so I figured all bees out of here.

BUT those wasps have never bothered me. I also lifted the wood off the yellow jacket nest, so hopefully they will go someplace else. I'll protect them, too -- and just keep fire wood from getting thrown haphazardly in the yard.